1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method for processing a substrate by use of liquids. Examples of substrates to be processed include semiconductor wafers, substrates for liquid crystal displays, substrates for plasma displays, substrates for FEDs (Field Emission Displays), substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photomasks, ceramic substrates, and substrates for solar cells.
2. Description of the Related Art
For example, a chemical liquid is supplied to a substrate substantially horizontally held by a spin chuck in a substrate processing operation that employs a single substrate processing type in which substrates are processed one by one. Thereafter, a rinse liquid is supplied to the substrate, and, as a result, the chemical liquid present on the substrate is replaced with the rinse liquid. Thereafter, a spin dry step of excluding the rinse liquid present on the substrate is performed.
As shown in FIG. 14 of Japanese Patent Application Publication No. 2010-177371, when a fine pattern is formed on the front surface of the substrate, a liquid surface (interface between air and the liquid) is formed inside the pattern in the spin dry step. In this case, the surface tension of the liquid acts on a contact position between the liquid surface and the pattern. If this surface tension is large, a pattern collapse is liable to occur. The surface tension of water, which is a typical rinse liquid, is large, and therefore the pattern collapse in the spin dry step is non-negligible.
Therefore, a technique has been proposed in which water that has entered the inside the pattern is replaced with IPA (isopropyl alcohol) by supplying IPA that is a low-surface-tension liquid lower in surface tension than water, and IPA is then removed, and, as a result, the front surface of the substrate is dried.
For example, a liquid film of IPA is formed by supplying IPA onto the upper surface of the substrate. Thereafter, a nitrogen gas is sprayed onto a central part of the upper surface of the substrate being rotated around a rotational center that passes through the central part of the substrate. Therefore, IPA is removed from the central part of the upper surface of the substrate, and, as a result, a hole is formed (Japanese Patent Application Publication No. 2010-177371). Thereafter, the inner diameter of the annular liquid film is enlarged by means of a centrifugal force generated by the rotation of the substrate or by means of a spraying force of the nitrogen gas. Therefore, the liquid film is excluded outwardly from the substrate, and, as a result, the front surface of the substrate is dried.
On the other hand, there is a case in which IPA is discharged from an IPA discharge nozzle while performing scanning by moving a nozzle head that has both the IPA discharge nozzle and a nitrogen gas discharge nozzle from the center of a substrate toward its peripheral edge (United States Patent Application Publication No. 2009/0205684 A1). As a result, the liquid film of IPA supplied to the substrate is pushed outwardly from the substrate by means of the centrifugal force and the spraying force of the nitrogen gas. Therefore, the front surface of the substrate is dried.